Tim did a great job, but I thought I'd add some suggestions.  The below assumes starting with the coin in the right hand:

1.  Show both hands, one empty and one with a coin.  The coin should be in the palm of your hand.

2.  Close both hands into a loose fist and start breathing heavy.  Act like you are psyching yourself up for the ordeal to follow.

3.  As you close your fist, make the coin jump to your fingers, first or second  joint, if you can do it.

4.  Slap your palms to your ear.  With the coin positioned properly it should now be behind your ear.

5.  As you make faces, writhe around, tilt your head this way and that.  Breathe hard, grunt, have a good time.  The occassional crazy smile and titter, as though the coin is tickling a particularly sensitive spot inside your brain might look good.

6.  As you tilt your head, tilt it so the audience can see your right hand, fingers extended - coin still hidden against your right skull behind your ear.  This misdirection lets them know your fingers "aren't involved."  Move your palm as though you are trying to push the coin with it.

7. Tilt your head back and away, close your fingers around your head and allow the coin to drop to your fingertips.  Feed the coin to the left hand.  Tip your head toward the left shoulder and the coin should drop easily into the left palm.  From here it's up to you how long you wish to drag out the agony - not for you but for your audience.

[In answer to comment #5:  Once the coin is placed in your fingers, not your palm, it should be plastered against your head by the pads of your finger.  Your ear, or at least my ear, is not so thick.  With the palm pushing your ear against your head, the first pad of the middle finger can easily keep it in place - and hidden - while extending the all the fingers straight back.  Once that side of your head is facing away from the spectator,  wrap your fingers around your head to continue with the trick.  Please refer to Tim Davis' original write-up if you have further questions.]

[In answer to other comments:  Remember that you can always present this without the contortions and sound effects.  Any performer, writer, etc. should know enough to consider the intended audience for his work.]